They can't stall forever on new web standards if they prove useful. I'm not sure WebGL will, but if it does, the "graceful degradation" culture in web development means that IE users will get some sort of slow, limited approximation of the intended experience. And enough of them will know and start installing Chrome or Firefox in larger numbers again.

Microsoft can slow the adoption of web standards (and just via the desktop), but they don't have any real control now. And the only reason WebGL isn't in IE 10 is because they didn't want to offend the DX/D3D team. Once IE supports WebGL, D3D will die.